#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
	write(1,"hello",5);
	sleep(2);
	//i/o write first,then sleep;

	fwrite("world",5,1,stdout);
	sleep(2);
	//i/o(biao zhun) sleep first ,then write 
}